Abstract. Ice supersaturation in the upper troposphere is a complex and important issue
for the understanding of cirrus cloud formation. On one hand, infrared
sounders have the ability to provide cloud properties and atmospheric
profiles of temperature and humidity. On the other hand, they suffer from
coarse vertical resolution, especially in the upper troposphere and therefore
are unable to detect shallow ice supersaturated layers. We have used data
from the Measurements of OZone and water vapour by AIrbus in-service airCraft
experiment (MOZAIC) in combination with Atmospheric InfraRed Sounder (AIRS)
relative humidity measurements and cloud properties to develop a calibration
method for an estimation of occurrence frequencies of ice supersaturation.
This method first determines the occurrence probability of ice
supersaturation, detected by MOZAIC, as a function of the relative humidity
determined by AIRS. The occurrence probability function is then applied to
AIRS data, independently of the MOZAIC data, to provide a global climatology
of upper-tropospheric ice supersaturation occurrence. Our climatology is then
compared to ice supersaturation occurrence statistics from MOZAIC alone and
related to high cloud occurrence from the Cloud-Aerosol Lidar with Orthogonal
Polarization (CALIOP). As an example of application it is compared to model
climatologies of ice supersaturation from the Integrated Forecast System
(IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) and
from the European Centre HAmburg Model (ECHAM4). This study highlights the
benefits of multi-instrumental synergies for the investigation of upper
tropospheric ice supersaturation.